---
title: Load Balancing
description: Cypress will automatically balance your spec files across the available machines in your CI provider.
sidebar_position: 30
---

<ProductHeading product="cloud" />

# Load Balancing

## Balance strategy

Cypress will automatically balance your spec files across the available machines
in your CI provider. Cypress calculates which spec file to run based on the data
collected from previous runs. This ensures that your spec files run as fast as
possible, with no need for manual configuration.

As more and more tests are recorded to the Cloud, Cypress can better predict how
long a given spec file will take to run. To prevent irrelevant data from
affecting the duration prediction, Cypress doesn't use old historical run data
regarding the spec file.

### Spec duration history analysis

<DocsImage
  src="/img/app/parallelization/load-balancing.png"
  alt="Spec duration forecasting"
/>

With a duration estimation for each spec file of a test run, Cypress can
distribute spec files to available CI resources in descending order of spec run
duration. In this manner, the most time-consuming specs start first which
minimizes the overall test run duration.

:::info

Duration estimation is done separately for every browser the spec file is tested
against. This is helpful since performance characteristics vary by browser, and
therefore it is perfectly acceptable to see different duration estimates for
each browser a spec file was tested against.

:::
